A polarizing element is an optical element that absorbs light polarized in one direction and transmits light polarized in a direction perpendicular to this direction. In principle, liquid-crystal displays are required to include polarizing elements. Particularly in the case of a liquid-crystal display that uses a high-intensity light source, such as a transmission-type LCD projector, a polarizing element needs to have excellent heat resistance due to being exposed to intense radiation, and is also demanded to have a size on the scale of a few centimeters and a high extinction ratio. Wire grid inorganic polarizing elements have been proposed in response to these demands (for example, refer to PTL 1 and 2).
A wire grid polarizing element has a structure in which many conductive wires (reflection layer) that extend in one direction are arranged on a substrate at a narrower pitch (tens of nanometers to hundreds of nanometers) than the operating wavelength band. When the polarizing element is irradiated with light, light that is polarized parallel to the extension direction of the wires (TE waves (S-waves)) cannot pass through the polarizing element, whereas light that is polarized perpendicularly to the extension direction of the wires (TM waves (P-waves)) can pass through the polarizing element. Wire grid polarizing elements have excellent heat resistance, can be made with a relatively large size, and have a high extinction ratio, which makes them suitable for LCD projector applications and the like.
For example, in the case of a wire grid polarizing element described in PTL 1, a grid structure layer in which protrusion-like lines are arranged at specific intervals is formed on a transparent substrate. The grid structure layer is formed from resin. Next, sputter etching is used to process tips of the protrusion-like lines into pointed shapes. Thereafter, oblique irradiation with metal particles is performed to form a metal layer around each tip of the grid structure layer made of resin.
In the case of a wire grid polarizing element described in PTL 2, metal wires are formed on a transparent substrate and then a dielectric layer and an absorption layer are provided thereon. Light polarized parallel to an extension direction of the wires (TE waves (S-waves)) is selectively absorbed by the dielectric layer and the absorption layer. By using this wire grid polarizing element in an LCD projector, it is possible to reduce deterioration of image quality caused by a ghost, or the like, generated when returning light that is reflected off the surface of the polarizing element is reflected again inside the LCD projector.
The TM wave (P-wave) transmittance of a polarizing element is preferably as high as possible. However, in the case of a conventional wire grid polarizing element, due to the relationship between the pitch and grid width, which is in accordance with the operating wavelength band, light transmittance decreases, in principle, toward shorter wavelengths from the design wavelength. In a visible light region used in an LCD projector (red band: wavelength λ=600 nm to 680 nm; green band: wavelength λ=520 nm to 590 nm; blue band: wavelength λ=430 nm to 510 nm), it is the blue band for which transmittance is lowest in the case of a polarizing element having a wavelength in the green band as a design wavelength. It is known that transmittance can be increased by making the grid width of a polarizing element narrower. However, in reality, it is difficult to form a pattern having a narrower grid width and it is also hard to ensure reliability.